Automotive vehicles are commonly equipped with air bags and other devices that are selectively enabled or disabled based upon a determination of the presence of an occupant in a vehicle seat. It has been proposed to place electrically conductive material in a vehicle seat to serve as an electrode for detecting the presence of an occupant in the seat. For example, U.S. Patent Application Publication No. 2009/0267622 A1, which is hereby incorporated herein by reference, describes an occupant detector for a vehicle seat assembly that includes an occupant sensing circuit that measures the impedance of an electric field generated by applying an electric signal to the electrode in the seat. The presence of an occupant affects the electric field impedance about the electrode that is measured by the occupant sensing circuit. Additionally, many vehicle seats are equipped with a seat heater which generally includes an electrically conductive mat for receiving the electrical current which, in turn, generates thermal energy to heat the seat. Moreover, the seat heater has circuit elements in the control circuitry which, such as transistors, may interfere with the accuracy of measuring the electric field impedance. What is needed is a system and method that can determine the presence of an occupant in a vehicle seat having an electrode that is not adversely affected by the seat heater and its control circuitry.